The present invention relates generally to attaching materials to concrete substrates. In particular the present invention relates to a self-drilling, self-tapping screw for light concrete blocks.
Concrete is a hard and friable substance difficult to penetrate and engage with a threaded fastener. The properties of concrete conventionally dictate that a clearance hole be provided before any fastener may be affixed to the concrete. Conventionally, when fastening an item to concrete block one typically first uses a carbide tipped drill to provide a clearance hole before a self-tapping fastener can be installed. After the hole is drilled with a drill bit in a hammer drill, a screw gun is used to install the screw. In some applications, a lead or plastic insert may be placed in the clearance hole before the screw is installed. While this process works well, it may be characterized by relatively high labor and material costs because the process involves several steps, multiple tools and frequently the handling and installation of multi-piece fasteners.
U.S. Pat. No. 4,034,641 to Williams et al discloses one type of self-drilling anchor to which the present invention generally relates. The self-drilling anchor has a driving head, a shank having a threaded portion and an unthreaded portion and a drill tip. A conventional drill tip at the end of the shank is defined by a taper and flutes. The unthreaded portion of the shank is forged in a configuration having major and minor diameters.
A drill tip capable of reliably penetrating concrete must be made of material having a hardness which typically renders the material too brittle to be used for the driving and holding functions required of the shank and head portions of the fastener. The unitary fastener composition of conventional related fasteners must compromise either the hardness constraints of the drill tip or the durability constraints of other parts of the fastener often leading to mechanical failure at either the head or shank or to an unnecessarily expensive fastener.